The present invention relates to optical devices for sensing substances in a solution, and more particularly concerns an optical sensor, an optical nose and a method of making the latter.
xe2x80x9cSmell-detectorsxe2x80x9d or xe2x80x9celectronic nosesxe2x80x9d are substance detecting devices based on a technique in full expansion which uses the absorption by polymeric membranes of analytes present in fluids. The absorption of the analytes by the polymeric membranes generates an alteration of its physical properties, such as density, thickness, refractive index, resistivity, etc.
Electronic techniques for measuring these alterations of the properties of the membrane are well documented. For example, the product named xe2x80x9cCyranose 320xe2x80x9d (trademark) from the company Cyrano Sciences Inc. is based on such a technique. Typically, an electronic nose is composed of many sensors made from different polymers, each having its own reaction to the presence of a given substance. Electronic noses generally measure the change in resistivity of the polymer membranes. However, since polymers are rarely conductive, it is usually necessary to mix conductive particles, for example carbon-black, to the polymeric material, thereby increasing the conductivity of the membrane. Another major drawback experienced by these devices is sensor drift, which creates the necessity for frequent calibration or xe2x80x9cretrainingxe2x80x9d of the sensors.
Optical based detecting techniques are also known in the art. In these cases, the luminescence of the polymeric membrane when exposed to a given analyte is measured and characterized. The following references study the various aspects of this technique: xe2x80x9cRandomly Ordered Addressable High-Density Optical Sensor Arraysxe2x80x9d Michael, K. L., Taylor, L. C. Schultz, S. L., Walt, D. R., Anal. Chem. 1998, 70, 1242-1248, xe2x80x9cThe Use of Optcal-Imagining Fibers for the Fabrication of Array Sensorsxe2x80x9d Michael, K. L., Ferguson, J. A., Healy, B. G., Panova, A. A., Pantano, P., Walt, D. R., American Chemical Society, 1998; 273-288; xe2x80x9cOrdered Nanowell Arraysxe2x80x9d Pantano, P., Waft, D. R., Chem. Mater. 1996, 8, 2832-2835; xe2x80x9cCombined imaging and chemical sensing of fertilization-induced acid release from single sea urchin eggsxe2x80x9d, Michael, K. L., Walt, D. R., Anal. Biochem., 1999, 273, 168-178; xe2x80x9cConvergent, Self-Encoded Bead Sensor Arrays in the Design of an Artificial Nosexe2x80x9d Dickinson, T. A., Michael, K. L., Kauer, J. S., Walt, D. R., Anal. Chem., 1999, 71, 2192-2198; xe2x80x9cidentification of Multiple Analytes Using an Optical Sensor Array and Pattern Recognition Neural Networksxe2x80x9d Johnson, S. R., Sutter, J. M., Engelhardt, H. L., Jurs. P. C., White, J, Kauer, J. S., Dickinson, T. A., Walt, D. R., Anal. Chem, 1997, 69, 4641-4648; xe2x80x9cA Chemical-Detecting System based on a cross-reactive optical sensor arrayxe2x80x9d, Dickinson, T. A., White, J., Kauer, J. S., Walt, D. R., Nature, 1996, 382, 697-700; and xe2x80x9cHigh-Speed Fluorescence Detection of Explosives Vaporxe2x80x9d. Albert, K. J., Myrick, M. L., Brown, S. B., Milanovich, F. P., Walt, D. R., SPIE, 1999, 3710, 308-314.
An object of the present invention is to provide a sensing device measuring the change in thickness of the polymer membrane by optical means.
Another object of the invention is to provide such a sensing device for either detecting a particular substance or identifying at least one substance in a solution.
Yet another object of the present invention is to provide a method for making such a device.
Accordingly, the present invention provides an optical sensor for detecting a substance in a solution, comprising:
an optical fiber having a free extremity;
a polymer layer deposited on said free extremity of the optical fiber, said polymer layer laying in a plane normal to a longitudinal axis of the optical fiber, the polymer layer having a thickness related to said substance when exposed thereto;
a light source coupled to the optical fiber for injecting an analytical light beam therein so that said analytical light beam is reflected by the polymer layer to define a reflected light beam; and
a spectrum analyzer coupled to the optical fiber for receiving the reflected light beam and analyzing said reflected light beam to deduce therefrom the thickness of the polymer layer.
In accordance with another object of the invention, there is provided an optical nose for identifying at least one substance in a solution, said optical nose comprising:
a plurality of optical sensors, each comprising an optical fiber having a free extremity and a polymer layer deposited on said free extremity, said polymer layer laying in a plane normal to a longitudinal axis of the optical fiber, at least two of said polymer layers being of different types, each polymer layer having a thickness related to said at least one substance when exposed thereto;
a light source, coupled to the optical fiber of each of the optical sensors, for injecting an analytical light beam therein so that said analytical light beam is reflected by the corresponding polymer layer to define a reflected light beam; and
a spectrum analyzer coupled to the optical fiber of each of the optical sensors, for receiving each of the reflected light beams, analyzing each of said reflected light beams to deduce therefrom the thickness of the corresponding polymer layer, and identifying the at least one substance corresponding to said thicknesses.
Also, the present invention provides a method of making an optical nose for identifying at least one substance in a solution, the method comprising the steps of:
a) providing a plurality of optical fibers, each having a free extremity;
b) depositing a polymer layer on the free extremity of each optical fiber in a plane normal to a longitudinal axis of the optical fiber, at least two of said polymer layers being of different types, each polymer layer having a thickness related to the at least one substance when exposed thereto;
c) coupling each of the optical fibers to a light source for injecting an analytical light beam therein, so that said analytical light beam is reflected by the corresponding polymer layer to define a reflected light beam;
d) coupling each of the optical fibers to a spectrum analyzer for receiving each of the reflected light beams and for analyzing each of said reflected light beams to deduce therefrom the thickness of the corresponding polymer layer; and
e) exposing-the optical nose to solutions including known substances and identifying the thicknesses of the polymer layers corresponding to said known substances.
Other features and advantages of the present invention will be better understood upon reading the following description of preferred embodiments thereof, with reference to the appended drawings.